Summary of Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues
Lime and limestone operations	$ 30,797	$ 36,452	$ 31,779	$ 29,362	$ 34,341	$ 37,855	$ 37,320	$ 35,051	$ 128,390	$ 144,567	$ 128,003
Natural gas interests	497	577	671	702	1,060	1,218	1,356	1,640	2,447	5,274	5,762
Revenues	31,294	37,029	32,450	30,064	35,401	39,073	38,676	36,691	130,837	149,841	133,765
Gross profit
Gross profit, Lime and limestone operations	5,575	10,320	6,809	5,697	7,321	9,271	9,704	7,662
Gross profit, Natural gas interests	(105)	47	204	167	572	612	719	930
Gross profit	5,470	10,367	7,013	5,864	7,893	9,883	10,423	8,592	28,714	36,791	30,800
Net income (loss)	$ 2,286	$ 5,676	$ 2,559	$ 2,365	$ 3,731	$ 5,426	$ 5,718	$ 4,492	$ 12,886	$ 19,367	$ 14,800
Basic income per common share (in dollars per share)	$ 0.41	$ 1.01	$ 0.46	$ 0.42	$ 0.67	$ 0.97	$ 1.03	$ 0.81	$ 2.30	$ 3.47	$ 2.66
Diluted income per common share (in dollars per share)	$ 0.41	$ 1.01	$ 0.46	$ 0.42	$ 0.67	$ 0.97	$ 1.03	$ 0.80	$ 2.30	$ 3.47	$ 2.66